Piezoelectric actuating device for controlling the flaps on the rotor blade of a helicopter

ABSTRACT

The invention relates to a piezoelectric actuating device for controlling the flaps on the rotor blade of a helicopter. The inventive device comprises a piezo element arrangement ( 2 ) and a power transmission frame ( 10 ) which is coupled therewith, is fixed to the rotor blade and generates a force between an abutment ( 14 ) and a driven element ( 13 ) by changing the length of the piezo element arrangement ( 2 ). Said force is effective crosswise in relation to the direction of the centrifugal force of the rotor blade. According to the invention, a first holder ( 11, 12 ) which fixes the power transmission frame ( 10 ) to the rotor blade in the direction of the centrifugal force and is flexible crosswise in relation to the direction of the centrifugal force and a second holder ( 15, 16 ) which fixes the abutment ( 14 ) that is provided on the power transmission frame ( 10 ) crosswise in relation to the direction of the centrifugal force and is flexible in the direction of the centrifugal force are provided. The inventive actuating device guarantees reliable and flawless operation even when the centrifugal forces which prevail on the rotor blade are high.

[0001] The present invention relates to a piezoelectric actuating devicefor controlling the flaps on the rotor blade of a helicopter, includinga piezo element arrangement that contains at least one piezoelectricstack actuator, and further including a transmission frame which iscoupled to the piezo element arrangement and attached to the rotor bladeand which generates a force between an abutment and a driven element,which are provided on the power transmission frame, from a change inlength of the piezo element arrangement upon excitation thereof, theforce acting transversely to the direction of the centrifugal force ofthe rotor blade.

[0002] Piezoelectric actuating devices are increasingly used in manyfields of application and can be used to advantage especially inaerospace due to their small size and their high power density. Becauseof their high power density, piezoelectric actuating devices areparticularly suitable for controlling the flaps on the rotor blades ofhelicopters. In this context, however, it is a problem that thepiezoelectric actuating device must be guaranteed to be securelysupported and decoupled against the centrifugal force (of up to 1000 g)occurring at the rotor blade.

[0003] German Patent DE 196 46 676 C1 and German Patent Application DE196 48 545 A1 describe piezoelectric stack actuators in the form ofstacked individual piezoelectric elements as could be provided in apiezo element arrangement contained in a piezoelectric actuating deviceand used for driving the same.

[0004] The object of the present invention is to provide a piezoelectricactuating device for controlling the flaps on the rotor blade of ahelicopter which features a high degree of performance reliability andoperational safety.

[0005] This objective is achieved according to the present invention bya piezoelectric actuating device having the features of claim 1.Advantageous embodiments of the actuating device according to thepresent invention are characterized in the subclaims.

[0006] The present invention provides a piezoelectric actuating devicefor controlling the flaps on the rotor blade of a helicopter, includinga piezo element arrangement that contains at least one piezoelectricstack actuator, and further including a power transmission frame whichis coupled to the piezo element arrangement and fixed to the rotor bladeand which generates a force between an abutment and a driven element,which are provided on the power transmission frame, from a change inlength of the piezo element arrangement upon excitation thereof, theforce acting transversely to the direction of the centrifugal force ofthe rotor blade. According to the present invention, the piezoelectricactuating device features a first holding device which fixes the powertransmission frame on the rotor blade in the direction of thecentrifugal force but is flexible transversely to the direction of thecentrifugal force and which allows the power transmission frame to movetransversely to the direction of the centrifugal force relative to therotor blade within a limited range as well as a second holding devicewhich fixes the abutment, which is provided on the power transmissionframe, transversely to the direction of the centrifugal force relativeto the rotor blade but is flexible in the direction of the centrifugalforce and which allows the abutment to move in the direction of thecentrifugal force relative to the rotor blade within a limited range.

[0007] The piezoelectric actuating device has the essential advantage ofbeing reliably and securely fixed against the high centrifugal forceoccurring at the rotor blade of a helicopter without thereby impairingthe performance reliability of the actuating device.

[0008] Advantageously, the first holding device includes first holdingelements which extend longitudinally in the direction of the centrifugalforce and which are attached to the rotor blade at one end and to thepower transmission frame of the actuating device at the other end. Theseguarantee that the power transmission frame is reliably supportedagainst the centrifugal force, the driven element and the abutment atthe same time being allowed to move without restriction in the mannerintended for this.

[0009] Preferably, the first holding elements are formed of straps whichare flexurally soft transversely to the direction of the centrifugalforce of the rotor blade. Such straps allow the power transmission frameto move without restriction transversely to the direction of thecentrifugal force, the power transmission frame at the same time beingreliably fixed in the direction of the centrifugal force. Moreover, theuse of such flexurally soft straps allows the power transmission frameto be fixed in the third direction as well, i.e., in a directionperpendicular to the plane defined by the direction of the centrifugalforce and the intended direction of motion of the abutment and thedriven element.

[0010] Preferably, the first holding device contains two arrangements offirst flexurally soft straps extending essentially parallel to eachother in the direction of the centrifugal force. This permits a quasiparallelogram movement of the flexurally soft straps relative to thepower transmission frame and relative to a centrifugal force fastenerwhich is provided on the rotor blade and to which the first holdingelements are fixed. In the simplest and preferred case, each of the twoarrangements of first flexurally soft straps contains only one suchstrap so that the power transmission frame is held by two first strapsrunning parallel to each other in the direction of the centrifugalforce.

[0011] On the side of the power transmission frame, the first holdingelements are advantageously attached to the abutment or in the vicinitythereof or to the driven element or in the vicinity thereof,respectively.

[0012] According to an expedient embodiment of the piezoelectricactuating device according to the present invention, the second holdingdevice includes second holding elements which extend transversely to thedirection of the centrifugal force and are connected to the abutment atone end and, at the other end, to a fastening element which is used forattachment to the rotor blade. This allows the power transmission frameof the actuating device to move in a defined manner in the direction ofthe centrifugal force so that power transmission frame is decoupled fromthe centrifugal force to the largest extent possible with regard to themotion of the driven element and the abutment relative to each other.

[0013] Preferably, the second holding elements are also formed offlexurally soft straps which here, however, are arranged in such amanner that they are flexible in the direction of the centrifugal forceof the rotor blade. This permits motion between the fastening elementand the abutment in the intended direction in the direction of thecentrifugal force, the power transmission frame, on the other hand,being fixed in a direction perpendicular to the plane defined by thedirection of the centrifugal force and the working direction between theabutment and the driven element.

[0014] Preferably, the second holding device contains two arrangementsof second flexurally soft straps extending essentially parallel to eachother transversely to the direction of the centrifugal force. This, inturn, permits a parallelogram movement between the fastening element andthe abutment; each of the two arrangements of second flexurally softstraps in the simples and preferred case containing only one such strapso that the second holding device is formed of two flexurally softstraps running essentially parallel to each other transversely to thedirection of the centrifugal force.

[0015] Preferably, the piezo element arrangement of the actuating devicecontains at least one piezoelectric stack actuator extendinglongitudinally in its working direction, and the power transmissionframe includes working yokes which are coupled to the respective ends ofthe piezo element arrangement as well as driven legs which connect theworking yokes and extend approximately parallel to the longitudinaldirection of the piezo element arrangement and which feature drivenregions in the form of the abutment and the driven element in a centralregion between the working yokes, the driven legs together with theworking yokes forming a flexible arrangement in terms of a displacementof the driven regions relative to each other in a directionperpendicular to the longitudinal direction of the piezo elementarrangement, the flexible arrangement converting an expansion andcontraction of the piezo element arrangement in its longitudinaldirection to a movement of the abutment and the driven element relativeto each other in a direction perpendicular to the longitudinal directionof the piezo element arrangement.

[0016] Preferably, the above mentioned embodiment is designed in such amanner that the piezo element arrangement is coupled with its ends tothe center of each working yoke, respectively, and that each workingyoke is provided with driven legs in pairs which oppose each other withrespect to the center of the respective working yoke and which are eachflexibly connected at one end to each side of a working yoke and which,at the other end, extend toward the driven regions in the form of theabutment and the driven element, respectively, which are located in thecentral region.

[0017] According to an embodiment of the piezoelectric actuating deviceaccording to the present invention, the driven legs are constituted byintrinsically rigid single legs which are hinged in the central regionand at the ends that are associated with the working yokes.

[0018] According to a preferred refinement thereof, in each case twoparallel, spaced apart driven legs are provided between each side of aworking yoke and a driven region in the form of the abutment or thedriven element, respectively, the driven legs performing aparallelogram-like movement during a movement of the abutment and thedriven element. The special advantage of this is an increased stabilityof the power transmission frame against the arising high centrifugalforces.

[0019] Preferably, the first holding elements are provided at their endwhich is intended for attachment to the rotor blade with fastening loopswhich are integrally formed with the first holding elements,

[0020] According to a particularly advantageous embodiment of thepiezoelectric actuating device, provision is made for the powertransmission frame, which includes the working yokes, the driven legs,and the driven regions in the form of the abutment and the drivenelement, to be manufactured in one piece together with the first holdingelements and the second holding elements, including the fasteningelements used for attachment to the rotor blade. This advantageouslyallows for inexpensive manufacture of a piezoelectric actuating deviceaccording to the present invention which features a high degree ofreliability and operational safety.

[0021] According to an alternative embodiment, the driven legs can beformed of a thin flexible strap material instead of in the form ofintrinsically rigid single legs, the strap material featuring a lowflexural stiffness in the direction of its thickness and a high rigidityin the transverse direction.

[0022] In the following, an exemplary embodiment of the presentinvention will be explained with reference to the drawing.

[0023]FIG. 1 shows a lateral view of a piezoelectric actuating deviceaccording to an exemplary embodiment of the present invention; and

[0024]FIG. 2 is a perspective view of the piezoelectric actuating deviceshown in FIG. 1 according to the exemplary embodiment of the presentinvention.

[0025] The piezoelectric actuating device which is shown in the lateralview in FIG. 1 and in the perspective view in FIG. 2 and which, as awhole, is provided with reference numeral 1, is essentially composed ofa piezoelectric stack actuator 2 and a power transmission frame which,as a whole, is provided with reference numeral 10. Piezoelectric stackactuator 2 is a longitudinally extending structure and formed of aplurality of individual piezoelectric elements which are arranged inlayers one over another, as is known per se. Power transmission frame 10is composed of two working yokes 8,9 which are coupled to respectiveends A and B of stack actuator 2 and of a number of driven legs 4 a,b, 5a,b, 6 a,b and 7 a,b, a driven element 13 and an abutment 14. Piezoelement arrangement 2 is coupled with its ends A,B to the center of eachworking yoke 8,9, respectively, working yokes 8,9 being wider than piezoelement arrangement 2 and projecting over piezo element arrangement 2 onboth sides. On both sides of each working yoke 8,9, driven legs 4 a,b, 5a,b and 6 a,b and 7 a,b are each attached in pairs with the one ends,respectively, the other ends of the driven legs being connected todriven element 13 or to abutment 14, respectively, namely the ends ofdriven legs 4 a,b and 6 a,b to driven element 13, and the ends of drivenlegs 5 a,b and 7 a,b to abutment 14. Power transmission frame 10generates a force between abutment 14 and driven element 13 from achange in length of piezo element arrangement 2 upon excitation thereof,the force acting transversely to the longitudinal extension of the piezoelement arrangement as is shown by the arrow at driven element 13. Whenpiezo element arrangement 2 expands longitudinally, driven element 13and abutment 14 are moved relative to and toward each other transverselyto the longitudinal extension of piezo element arrangement 2. Acontraction of piezo element arrangement 2 reverses the describedmovement.

[0026] Longitudinally extending first holding elements 111,12 in theform of flexurally soft straps which are provided with fastening loops17 and 18 at their ends are provided on power transmission frame 10,namely at driven element 13 and at abutment 14. The piezoelectricactuating device, which is designed for controlling the flaps of therotor blade, is attached to the rotor blade of a helicopter via thesefirst holding elements 11,12. The attachment is accomplished in such amanner that first holding elements 11,12 extend with their longitudinaldirection parallel to the direction of the centrifugal force of therotor blade. Using first holding elements 11,12, therefore, a firstfixing is accomplished which fixes power transmission frame 10 on therotor blade in the direction of the centrifugal force but is flexibletransversely to the direction of the centrifugal force and which allowspower transmission frame 10 to move transversely to the direction of thecentrifugal force relative to the rotor blade within a limited range(the centrifugal force is represented by arrows in FIGS. 1 and 2).

[0027] Also provided are second holding elements 15, 16 in the form offurther flexurally soft straps which are connected to abutment 14 at oneend and, at the other end, to a fastening element 19 which is used forattachment to the rotor blade. Second flexurally soft holding elements15,16 extend essentially parallel to each other transversely to thedirection of the centrifugal force of the rotor and fix powertransmission frame 10 transversely to the direction of the centrifugalforce relative to the rotor blade but are flexible in the direction ofthe centrifugal force and allow abutment 14 to move in the direction ofthe centrifugal force relative to the rotor blade within a limitedrange.

[0028] Driven legs 4 a,b, 5 a,b, 6 a,b, 7 a,b are constituted byintrinsically rigid single legs which, in the central region, namely atdriven element 13 and at abutment 14 as well as at working yokes 8,9,are hinged to the mentioned elements. Between each side of a workingyoke 8,9 and abutment 14 or driven element 13, respectively, provisionis made in each case for two driven legs, namely driven legs 4 a and 4b, 5 a and 5 b, 6 a and 6, and 7 a and 7 b, respectively, which are ineach case parallelly spaced apart from each other and which perform aparallelogram-like movement during a movement of abutment 14 and drivenelement 13.

[0029] Via first holding elements 11,12 and second holding elements15,16, power transmission frame 10 is, on one hand, reliably andsecurely fixed against the high centrifugal force acting on the rotorblade, which can amount to up to 1000 g; on the other hand, drivenelement 13 and abutment 14 have sufficient degrees of freedom so thatthese two elements are sufficiently decoupled from the centrifugal forceas well as from fastening elements 17, 18, 19 to be able to work withoutbeing unfavorably influenced.

[0030] In the exemplary embodiment shown in FIGS. 1 and 2, first holdingelements 11,12 are integrally formed with the fastening loops 17, 18 attheir ends which are intended for attachment to the rotor blade, andworking yokes 8,9, driven legs 4 a,b, 5 a,b, 6 a,b, 7 a,b, and thedriven regions in the form of abutment 14 and driven element 13, whichtogether form power transmission frame 10, are formed in one piecetogether with first holding elements 11,12 and second holding elements15,16, including fastening element 19 which is used for attachment tothe rotor blade.

[0031] List of Reference Numerals

[0032]1 piezoelectric actuating device

[0033]2 piezoelectric stack actuator

[0034]3

[0035]4 a,b driven leg

[0036]5 a,b driven leg

[0037]6 a,b driven leg

[0038]7 a,b driven leg

[0039]8 working yoke

[0040]9 working yoke

[0041]10 power transmission frame

[0042]11 first holding element

[0043]12 first holding element

[0044]13 driven element

[0045]14 abutment

[0046]15 second holding element

[0047]16 second holding element

[0048]17 fastening loop

[0049]18 fastening loop

[0050]19 fastening element

What is claimed is:
 1. A piezoelectric actuating device for controllingthe flaps on the rotor blade of a helicopter, comprising a piezo elementarrangement that contains at least one piezoelectric stack actuator (2),and further comprising a power transmission frame (10) which is coupledto the piezo element arrangement and attached to the rotor blade andwhich generates a force between an abutment (14) and a driven element(13), which are provided on the power transmission frame, from a changein length of the piezo element arrangement upon excitation thereof, theforce acting transversely to the direction of the centrifugal force ofthe rotor blade, characterized by a first holding device (11, 12) whichfixes the power transmission frame (10) on the rotor blade in thedirection of the centrifugal force but is flexible transversely to thedirection of the centrifugal force and which allows the powertransmission frame (10) to move transversely to the direction of thecentrifugal force relative to the rotor blade within a limited range;and a second holding device (15, 16) which fixes the abutment (14),which is provided on the power transmission frame (10), transversely tothe direction of the centrifugal force relative to the rotor blade butis flexible in the direction of the centrifugal force and which allowsthe abutment (14) to move in the direction of the centrifugal forcerelative to the rotor blade within a limited range.
 2. The piezoelectricactuating device as recited in claim 1, wherein the first holding deviceincludes first holding elements (11, 12) which extend longitudinally inthe direction of the centrifugal force and which are attached to therotor blade at one end and to the power transmission frame (10) of theactuating device at the other end.
 3. The piezoelectric actuating deviceas recited in claim 2, wherein the first holding elements (11, 12) areformed of straps which are flexurally soft transversely to the directionof the centrifugal force of the rotor blade.
 4. The piezoelectricactuating device as recited in claim 3, wherein the first holding device(11, 12) contains two arrangements of first flexurally soft strapsextending essentially parallel to each other in the direction of thecentrifugal force.
 5. The piezoelectric actuating device as recited inclaim 2, 3 or 4, wherein on the side of the power transmission frame,the first holding elements (11, 12) are attached to the abutment (14) orin the vicinity thereof or to the driven element (13) or in the vicinitythereof, respectively.
 6. The piezoelectric actuating device as recitedin one of the claims 1 through 5, wherein the second holding deviceincludes second holding elements (15, 16) which extend transversely tothe direction of the centrifugal force and are connected to the abutment(14) at one end and, at the other end, to a fastening element (19) whichis used for attachment to the rotor blade.
 7. The piezoelectricactuating device as recited in claim 6, wherein the second holdingelements (15, 16) are formed of straps which are flexurally soft in thedirection of the centrifugal force of the rotor blade.
 8. Thepiezoelectric actuating device as recited in claim 7, wherein the secondholding device (15, 16) contains two arrangements of second flexurallysoft straps extending essentially parallel to each other transversely tothe direction of the centrifugal force.
 9. The piezoelectric actuatingdevice as recited in one of the claims 1 through 8, wherein the piezoelement arrangement contains at least one piezoelectric stack actuator(2) extending longitudinally in its working direction; and the powertransmission frame (10) includes working yokes (8, 9) which are coupledto the respective ends (A, B) of the piezo element arrangement (2, 3) aswell as driven legs (4 a) which connect the working yokes and extendapproximately parallel to the longitudinal direction of the piezoelement arrangement (2) and which feature driven regions in the form ofthe abutment (14) and the driven element (13) in a central regionbetween the working yokes (8, 9), the driven legs (4 a, 4 b, 5 a, 5 b, 6a, 6 b, 7 a, 7 b) together with the working yokes (8, 9) forming aflexible arrangement in terms of a displacement of the driven regionsrelative to each other in a direction perpendicular to the longitudinaldirection of the piezo element arrangement (2), the flexible arrangementconverting an expansion and contraction of the piezo element arrangement(2, 3) in its longitudinal direction to a movement of the abutment (14)and the driven element (13) relative to each other in a directionperpendicular to the longitudinal direction of the piezo elementarrangement (2).
 10. The piezoelectric actuating device as recited inclaim 9, wherein the piezo element arrangement (2) is coupled with itsends (A, B) to the center of each working yoke (8, 9), respectively; andeach working yoke (8, 9) is provided with driven legs (4 a, 4 b, 5 a, 5b, 6 a, 6 b, 7 a, 7 b) in pairs which oppose each other with respect tothe center of the respective working yoke (8, 9) and which are eachflexibly connected at one end to each side of a working yoke (8, 9) andwhich, at the other end, extend toward the driven regions in the form ofthe abutment (14) and the driven element (13), respectively, which arelocated in the central region.
 11. The piezoelectric actuating device asrecited in claim 9, or 10, wherein the driven legs (4 a, 4 b, 5 a, 5 b,6 a, 6 b, 7 a, 7 b) are constituted by intrinsically rigid single legswhich are hinged in the central region and at the ends that areassociated with the working yokes (8, 9).
 12. The piezoelectricactuating device as recited in claim 11, wherein between each side of aworking yoke (8, 9) and a driven region in the form of the abutment (14)or the driven element (13), respectively, provision is made in each casefor two driven legs (4 a and 4 b, 5 a and 5 b, 6 a and 6, and 7 a and 7b) which are in each case parallelly spaced apart from each other andwhich perform a parallelogram-like movement during a movement of theabutment (14) and the driven element (13).
 13. The piezoelectricactuating device as recited in one of the claims 2 through 12, whereinthe first holding elements (11, 12) are provided at their end which isintended for attachment to the rotor blade with fastening loops (17, 18)which are integrally formed with the first holding elements 811, 12).14. The piezoelectric actuating device as recited in one of the claims 9through 13, wherein the power transmission frame (10), which includesthe working yokes (8, 9), the driven legs (4 a, 4 b, 5 a, 5 b, 6 a, 6 b,7 a, 7 b), and the driven regions in the form of the abutment (14) andthe driven element (13), is manufactured in one piece together with thefirst holding elements (11, 12) and the second holding elements (15,16), including the fastening element (19) which is used for attachmentto the rotor blade.
 15. The piezoelectric actuating device as recited inone of the claims 1 through 14, wherein the driven legs (4 a, 4 b, 5 a,5 b, 6 a, 6 b, 7 a, 7 b) are formed of a thin flexible strap materialwhich features a low flexural stiffness in the direction of itsthickness and a high rigidity in the transverse direction.